Various methods have been used to control devices downhole primarily on drill strings to cause an action to be carried out as a result of an initiating action at the earth surface, usually at the rig floor. Balls dropped down the drill string bore were used to cause an action, usually not reversible until the drill string was removed from the borehole to recover the dropped ball and reset the influenced device.
Spears were dropped down the well bore to cause a bend to take place in the drillstring. The spear could be adapted to be recovered by wire line run down the drill string bore. This was quite effective and was a reversible action, but time was invested in the wire line trip. This reduced the frequency with which the drilling crews were willing to exercise the controlled device.
As mud pulse communication came into common use for measurement while drilling, the term downlink command came into common use to describe any form of communication initiated at the earth surface to cause a preferred action to take place downhole. The U.S. Pat. No. 3,967,680 was issued July 6, 1976, to cause actions downhole as a result of selecting first to rotate the drill string, then start fluid flow to cause one action. The procedure was reversed to cause an alternate action to take place. After the first selected procedure activated the downhole selector, the pipe could be repeatedly started and stopped to select additional choices of action.
U.S. Pat. No. 3,896,667 was issued July 29, 1975, to control downhole devices by action of the fluid flow alone. To execute a downlink command, an intermediate fluid flow was selected, lower than the flow needed for drilling, and the flow rate was held until a timer ran a specific period before the elected action would take place. Many choices could be exercised. A different flow rate, held for a selected length of time, could cancel encoded actions and return to normal drilling configuration. This device generated a pulse signal to indicate the downlink command had been received and acted upon.
It is desirable to have a responsie device downhole that will change state each time the fluid flow down the string is initiated. If an action is not needed but is responsive to the onset of fluid flow, the flow can be stopped and restarted to select the alternate state downhole. One such apparatus to be controlled is the apparatus of my copending patent application 784,261. Feedback information is needed to assure that there is no risk of confusion as to which state is activated.
Apparatus of this invention has recently been used in downhole drilling related activities to actuate the apparatus of my copending application No. 784,261.